The invention relates to a method of and to an apparatus for testing circuit boards, integrated circuits, wired circuits, chips and like components which are provided with arrays of electric contacts. More particularly, the invention relates to improvements in methods of and in apparatus for testing circuit boards and like components with flexible test probes. Still more particularly, the invention relates to improvements in methods of and in apparatus for testing circuit boards and like components with test probes which are installed in an adapter serving as a means for connecting the contacts of the component to be tested with the conductors of a testing unit.
German Offenlegungsschrift No. 31 23 627 to Brabetz et al. discloses an adapter wherein an array of flexible resilient test probes, called pins, is installed in a housing having a front wall with holes for the front ends of the pins, a rear wall which is secured to the rear ends of the pins, and a mobile intermediate wall, called flexing plate, which is disposed between the front and rear walls and has openings slidably receiving median portions of the pins. The front end portions of the pins are slidable in the front wall and their tips serve to engage the adjacent contacts (e.g., contacts in the form of so-called pads) on a circuit board or a like component which is positioned adjacent the front wall. The housing contains a stop for the flexing plate, and the position of the stop is selected in such a way that the flexing plate maintains the pins in deformed condition when it is permitted to abut the stop. This ensures that the deformed resilient pins tend to dissipate energy and urge the tips of their front end portions into engagement with the contacts of the component to be tested. The flexing plate is moved away from the stop in response to depression of the tips of front end portions of pins by the contacts of a component to be tested whereby the pins store energy and tend to move the flexing plate back toward the stop. When the testing operation is completed and the distance of the front plate of the adapter housing from the freshly tested component is increased, the pins are free to dissipate energy and to return the flexing plate into engagement with the stop. As mentioned above, the flexing plate compels the pins to store a certain amount of energy when the adapter is not in use because the flexing plate is arrested by the stop before any of the pins can assume its unstressed condition.
It is normally desirable to ensure that the tips of the front end portions bear upon the adjacent contacts with a relatively large force because this ensures the establishment of reliable electrical connections between the contacts and the respective inputs of the testing unit. In order to ensure the establishment of reliable electrical connections, it is often necessary that the tips penetrate through oxide layers and/or through layers of contaminants at those sides of the contacts which confront the adjacent pins. As a rule, an adapter will comprise at least several hundred and often many thousand pins; therefore, it is necessary to exert upon the tips of the front end portions of pins a very large force which should ensure that the tips will indeed penetrate through layers of oxide and/or through layers of contaminants for the purpose of establishing a reliable electrical connection between each contact and the adjacent pin. Such forces are normally applied by a strong and large motor which is designed to move the housing of the adapter toward the component to be tested and/or vice versa. The motor contributes significantly to the initial and maintenance cost as well as to the bulk of the adapter of Brabetz et al.